1. Field of the Invention
This invention relates to apparatus used in cooking devices, i.e., ovens of the type employing heat elements to cook the food through a convective and conductive heat transmitting cooking process. More particularly, the invention concerns apparatus for maximizing the transfer of heat and mass during the cooking process so that relative cooking times of foods are reduced.
2. Description of the Prior Art
In ovens of the aforementioned type, a film or thin layer of stagnant air is known to adherently form at outer exposed food surfaces during the cooking process. This film acts as an insulator that effectively impedes rapid transfer of heated air molecules to the food. Conversely, rapid transfer of mass molecules, i.e., moisture, away from the food is also restricted by this insulating film. Consequently, the overall cooking efficiency of the oven is hindered by the formation of the stagnant layer of air.
Ways of improving heat transfer to overcome the thermal insulating problem posed by the film are addressed in the prior art. A particular solution to this problem is suggested in U.S. Pat. No. 4,238,668, granted to H. William Mammen on Dec. 9, 1980. Mammen discloses an oven fixedly equipped with a pair of fixed conductive guide ledges operatively maintained at a fixed--non-variable--DC potential. A conductive field grid element is maintained at a different fixed--non-variable--DC potential with respect to the ledges. A conductive food supporting rack or tray removably bridges the guide ledges so that an electrical field is created between the field grid element and the food on the rack or tray during the cooking process. The field grid element and the ledges are operated at different potentials for supporting current flow in the field. The grid element is made manually adjustable to accommodate different food sizes. Adjustment of the field grid element is made prior to cooking, and after it is adjusted, the grid element remains stationary in the oven throughout the cooking process.
The apparatus taught in Mammen improves heat transfer in conventional ovens. However, it suffers from a number of deficiencies among which is the requirement that the operator at least check and if needed to make the adjustment of the grid element prior to all cooking operations. This responsibility is a nuisance and a burden for the operator. Another disadvantage is that there are no practical means provided for moving the grid element to compensate for foods that change in volume during the cooking process, e.g., bread dough that rises. Yet another deficiency is attributed to the failure of Mammen to recognize the importance of maintaining constant current in the field to maximize the heat and mass transfer. This is evident because he fails to disclose voltage adjusting means that automatically changes the field current to compensate for electrical impedance in the field air that is changing during the cooking process. Consequently, maximum heat transfer is not accomplished during the entire cooking duration. Still another deficiency resides in the improved heat transfer apparatus being only applied at one food surface. This allows the heat retarding film to form along the remaining food surfaces to restrict heat transfer at those surfaces.
From the foregoing, it is understood that apparatus of the prior art falls short of providing maximum heat and mass transfer performance. In view of the prior art deficiencies, it is further understood that there is a need to make a more efficient heat and mass transfer apparatus which is more convenient for the operator to use.